1. Field of the Invention
The field of art to which the claims invention pertains is solid-bed adsorptive separation with an adsorbent comprising a zeolite. More specifically, the claimed invention relates to an improved process for the separation of cresol isomers by employing a solid crystalline aluminosilicate adsorbent which selectively removes para-cresol from the feed mixture. The para-cresol is then recovered from the adsorbent through a desorption step which employs a desorbent material containing an alcohol.
2. Description of the Prior Art
It is known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon species from mixtures thereof. In particular, the separation of normal paraffins from branched chained paraffins can be accomplished by using the type A zeolites which have pore openings from 3 to about 5 Angstroms. Such a separation process is disclosed for example in U.S. Pat. Nos. 2,986,589 and 3,201,491. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the crystalline aluminosilicate adsorbent, while excluding the larger or branched chain molecules.
U.S. Pat. Nos. 3,265,750 and 3,510,423 for example disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons.
The type X or type Y zeolites have additionally been employed in processes to separate individual hydrocarbon isomers. In the process described in U.S. Pat. Nos. 3,558,730; 3,558,732; 3,626,020; and 3,686,342, for example, they are used to separate desired xylene isomers; in U.S. Pat. No. 3,668,267 they are used to separate particular alkyl substituted naphthalenes.
More specifically, U.S. Pat. No. 3,014,078 teaches the separation of cresol isomers by employing an adsorbent consisting of a crystalline zeolitic metallo aluminosilicate to selectively adsorb a cresol isomer from a feed mixture thereby producing a rich adsorbent. In the preferred mode of operation, the adsorbed isomer is then removed by contacting with a displacement exchange fluid. A preferred displacement exchange fluid is phenol although other materials which may be employed include ethers, aromatic hydrocarbons, and paraffin hydrocarbons.
The present invention relates to an improved process for separating for the separation of cresol isomers. In particular we have found that employing a desorbent material comprising an alcohol to remove the selectively adsorbed para-cresol isomer from the zeolitic adsorbent increases the selectivity of the adsorbent for para-cresol with respect to the other cresol isomers thereby permitting a more efficient separation with a higher purity extract stream recovered from the process.